1. Field of the Invention
The present invention relates to a human s-myc-like polypeptide (hereinafter often referred to as MycL2) which is effective for the treatment of tumors, especially glioma and lung cancer, and to a human s-myc-like polypeptide gene (hereinafter often referred to as mycL2) coding for the amino acid sequence of said polypeptide.
2. Description of the Related Art
From a standpoint that a cause of a cancer or a tumor already exists in genome DNA of normal cells, a gene that gives an instruction of oncogenesis of the cells to cause the development and growth of a cancer or a tumor is termed an oncogene. In the specification, a myc gene is treated as an oncogene.
As an oncogene that causes gene amplification in various tumors such as human leukemia, lung cancer, gastric cancer, etc., c-myc is known and this oncogene forms a series of oncogene family together with N-myc, L-myc, V-myc, etc.
Apart of these oncogenes which cause the development and growth of a cancer or a tumor, s-myc gene is known to be a carcinostatic gene having an activity of preventing the growth of a cancer or inducing apotosis (programmed death of cells) of tumor cells.
The s-myc gene is a myc-associated gene first isolated and identified from a rat gene library in 1989, which is an intron-free genetic DNA encoding the amino acid sequence of a nucleoprotein (s-Myc) consisting of 429 amino acids (Sugiyama et al., Proc. Natl. Acad. Sci. USA, 86, 9144-9148 (1989)).
On the other hand, studies have also been made on a new method for transfection which comprises inserting a specific DNA into an expression vector for animal cells, embedding this expression vector in the inside of liposome composed of a synthetic cationic lipid, and transfecting the expression vector into tumor cells or into a living body together with the tumor cells thereby to effect the insertion and expression of the DNA (hereinafter referred to as lipofection or liposome-mediated transfection, see Felgner et al., Proc. Natl. Acad. Sci. USA, 84, 7413-7417 (1987)).
In particular, it is reported that the liposome-mediated transfection exhibits, when applied to a rat s-myc gene, therapeutic effects specific to a glioma which is one of brain tumors. Recently, attention has thus been brought to the liposome-mediated transfection as a promising treatment for intractable tumor diseases coupled with a genetic treatment in vivo.
However, human s-Myc-like polypeptide showing a carcinostatic action or apotosis-inducing activity against tumor has not yet been found and its isolation and identification have been desired (hereinafter these activities possessed by this peptide are collectively referred to as a human s-Myc-like polypeptide activity and this polypeptide is referred to as MycL2). Furthermore, mycL2 gene coding for the amino acid sequence of the polypeptide is yet unknown. It has thus been strongly desired to isolate and identify the aforesaid gene and to develop a pharmaceutical composition and method for the treatment of a tumor having a high specificity.